Traditional methods of estimating regional ventricular function for the most part involve measurement of simple dimension changes: eg. absolute or percent wall thickening. Such measures are limited in their application because they fail to account for loading conditions, and because they usually require a global parameter to time regional end-systole, such as LV dP/dt. We have studied the end-systolic pressure-thickness relationship (ESPTR) as an alternative measure of regional function. We have demonstrated its relative load-independence and its lack of dependence on global parameters to time regional end-systole. The overall aim of this project is to further explore and exploit the ESPTR as a measure of regional function. From a methodologic viewpoint we will determine: (a) if the brief change in coronary perfusion pressure attending measurement of the ESPTR affects the measurement itself; (b) if loading conditions altered with aortic occlusion result in an ESPTR different from that obtained with inferior vena cava occlusion; (c) the extent to which baroreceptor reflex effects influence cardiac contractile state; (d) if wall thickness data obtained using M-mode echocardiography can be used to construct the ESPTR, providing a non-surgical method of making this measurement of regional function; (e) if the ESPTR can be measured in intact conscious dogs. The ESPTR potentially provides a method for estimating changes in regional myocardial oxygen consumption. We will determine: (a) the relationship between pressure-thickness area (defined as the area bounded by the ESPTR, the diastolic pressure-thickness relation and a pressure-thickness loop) and regional myocardial oxygen consumption; and (b) how this relationship changes with alteration of contractile state. Finally, we will continue our study of ventricular compensatory mechanisms during acute regional ischemia. In particular, we will determine if, during acute regional ischemia: (a) the increased wall thickening of non-ischemic myocardium is due to a change in contractile state or loading conditions; and (b) if in spite of apparent hyperfunction of non-ischemic myocardium there is, in fact, a depression of cardiac contractile performance in this region. In summary, the ESPTR is a better index of regional function than simple dimension change measures. It has potential application to the study of regional function in humans, particularly in settings (eg. treatment of heart failure or ischemia) in which pharmacologic interventions may alter loading conditions, contractile state or the timing of systolic events.